The present invention relates generally to the field of torque tools and more particularly to a unique attachment for use with such tools for measuring and limiting the torque developed thereby in a manner which permits a greater degree of control with fewer wear parts than has been heretofore been attainable.
A wide variety of torque tools have been developed and are commercially available. For example electrically powered and air-powered torque wrenches are in common use. Some tools often include means for limiting the amount of torque developed by the tool so that the object being driven thereby will be torqued to a degree short of the force which would shear the member upon which the driven object is applied. Such mechanisms include governor controls and stall arrangements. Still others such as impact wrenches include means for alternately supplying and releasing the torque in order to reduce the reaction torque sensed by the operator of the tool.
The prior art reveals various types of control systems for controlling the amount of torque applied to a fastener. One common type employs a torque control in which the wrench tightens the fastener to a maximum predetermined value of torque and thereupon shuts off. Examples of various forms of such torque control are found in U.S. Pat. Nos. 4,316,512; 4,281,538; 4,199,032; 4,060,137; 4,006,784; 3,969,810; 3,835,934; 3,833,068; 3,703,933; 3,174,559; 3,018,866 and 2,543,979.
Another system of controlling wrenches found in the prior art is generally known as a "turn-of-the-nut" system in which a fastener is tightened to a preselected initial condition and thereafter rotated an additional predetermined number of degrees before sutting off. Examples of these systems are found in U.S. Pat. Nos. 3,623,557; 3,318,390 and 3,011,479.
Still another type of control involves imparting a constant angular momentum to each impluse blow as is shown in U.S. Pat. No. 3,181,672.
Each of the foregoing suffered disadvantages such as relatively slow operation and relatively inaccurate measurement of the applied torque. Still other systems place the control mechanism in position to receive the shock created by the impulse action of the tool. These mechanisms were readily damaged and maintenance and replacement costs were high.